Describe relational databases in detail. Why do we mostly use relational databases in the industry?
A relational database consists of a collection of tables in which each is assigned a unique name. The tables represent both data and the relationship among those data. In each table you find multiple columns and each column has a unique name. A relation is a two-dimensional table in which the following attributes, entries in a table are single-valued; each location contains a single value. Each column has its own distinct name and the values in each column must match the column name. The columns order is immaterial, ...view middle of the document...
The SQL standard is supported by all major database vendors, but the implementation of the full standard in all cases is not a guarantee. The common workhorse functions are the same in most cases. Databases change over time as information is inserted and deleted. The collection of information stored in the database at a particular moment is called an instance of the database. The overall design of the database is called the database schema. Schemas are changed infrequently, if at all.
Underlying the structure of a database is the data model. This is a collection of conceptual tools for describing data, data relationships, data semantics, and consistency constraints.
Data models can be classified in four categories:
One. Relational Model. This model uses a collection of tables to represent both data and the relationship among those data.
Two. Entity Relationship Model. This is based on a perception of a real world that consists of a collection of basic objects, called entities, and of relationships among these objects.
Three. Object-Based Data Model. This model extends the Entity Relationship Model with notions of encapsulation, methods, and object identity.
Four. Semistructured Data Model. This permits the specification of data where individual data items of the same type may have different sets of attributes.